Our studies aim at: a) identification of the most useful circadian schedules for the administration of antimetabolites in experimental and clinical cancer chemotherapy. b) Identification of basic differences in the circadian distribution of mitoses of normal and neoplastic cells, primarily in terms of circadian phase shifts which have been determined to occur in normal tissues in response to dexamethasone and isoproterenol. For these purposes, chemotherapy will be carried out in normal and tumor bearing mice and rats in which the circadian mitotic rhythm will be identified with the aid of biochemical and histological techniques: H3 Thymidine incorporation into DNA and mitotic index determinations. BIBLIOGRAPHIC REFERENCES: S. S. Cardoso, K. M. H. Philippens, I. Sauerbier, R. Bathacharya, T. Avery and H. von Mayersbach. Abstract. FASEB Anaheim, California, 1976. S. S. Cardoso, K. Philippens, T. Avery, C. King, P. Cruze and H. von Mayersbach. Proc. Third International Symposium on Detection and Prevention of Cancer. New York, April 26 to May 1, 1976, in press.